Abstract: photovoltaic power generation systems and networks is the trend of development of photovoltaic systems. According to photovoltaic power generation system and network characteristics, designed a 500 W power rating for the network and photovoltaic inverter, and the network inverter to achieve the maximum power to track and control the anti-island effect, based on some control TMS320F240 the current DSP-based tracking control strategy, and achieved a net pressure synchronized sine current output.
Key words: solar energy, photovoltaic systems; maximum power point tracking; island effect, and net inverter
1 INTRODUCTION
Solar large-scale application of the 21st century mankind will be an important indicator of social progress, and photovoltaic power generation systems and networks is the development trend of photovoltaic systems. Photovoltaic power generation systems and networks is not the biggest advantages of energy storage batteries, thus saving the investment, simplify the system and easy to maintain. This type of photovoltaic power generation systems and networks for peak shaving the main power plant and photovoltaic roof photovoltaic system. At present, the United States, Japan, the European Union and other developed countries have introduced a corresponding photovoltaic roof plan, submitted by Japan to 2010 to a total installed total capacity of 50 000MW home photovoltaic power stations. Rooftop photovoltaic system as the core network and the development of inverter industry has received increasing attention [1].
2 photovoltaic systems and network design
2.1 system architecture
PV inverters and the network structure as shown in Figure 1. PV inverters and network mainly by two components: the former level DC-DC converters and post-DC-AC inverter. Part 2 of this connected through DClink, DClink the voltage of 400 V. In this system, solar panels are rated for DC output voltage 100 V ~ 170V. DC-DC converters used boost structure, DC-AC part of a full-bridge inverter, control circuit is the core of TMS320F240-DSP. One DC-DC converters complete control of the maximum power tracking (MPPT) function, DC-AC inverter to maintain DClink intermediate voltage stability and power into the sine AC 220 V/50Hz. Network systems and ensure that the sine inverter output current and voltage of the grid with the same frequency and phase.
2.2 control circuit design
TMS320F240 control panel shown in Figure 2 to TI's DSP-TMS320F240 as the core, supplemented by external analog signal processing circuit, CPLD, and the DA digital display, communications and serial E2PROM, voltage and current signals the completion of the sampling, PWM Pulse production of PC and the communications and fault protection.
2.2.2 voltage and current signal detection circuit
Analog signal detection circuit is the function of the DSP strong signals can be read into the weak digital signals, to ensure strong and weak, the isolation. I choose HP's HCPL7800A-Optocoupler, the nonlinearity of 0.004 percent, a total of l 000V mode voltage for the common mode in capacity for 15 kV / l μ s, temperature drift to gain 0.000 25V / ℃, bandwidth 100kHz. Detection of specific isolation circuit as shown in Figure 3.
2.2.3 IGBT drive circuit
DSP control circuit of the PWM signal through the first drive circuit, and then switch IGBT control of the opening of state. I choose HP's exclusive HCPL3120-IGBT drive circuit, shown in Figure Drive circuit is the input and output isolation of each other, still driving circuit level translation function, the DSP +5 V control voltage converter for the +15 V IGBT drive voltage, drive circuit used the power of the Sun B0515 Isolation of power modules.
2.2.4 auxiliary power
In order to PV inverters and network control circuits, and signal acquisition circuit interrupters drive circuit to provide all kinds of work such as power, and the need to design a main circuit isolation of auxiliary power. The auxiliary power input voltage to 100 VDC ~ 170VDC; voltage output of the three routes were +15 VDC (2.5W),-15VDC (2.5W) and +5 VDC (5W); output voltage fluctuations of less than one percent. I use the latest Topswitch FOP222 series of auxiliary power circuit design [3]. Auxiliary power main circuit used single-ended flyback topology, as shown in Figure 5.
3 maximum power tracking control MPPT
MPPT, in essence, is a self-optimizing process [4], commonly used method of tracking a fixed voltage, the disturbance observer, admittance by law and the occasional micro-track scanning method. 。 I used to track scanning method is intermittent. Its core idea is scanning for some time (normally 0.5 times to 0.9 times the open circuit voltage an array voltage, while the corresponding records of different voltage output value of the array, and then compare different points of the output power of solar arrays, draw Maximum Power Point. The author of intermittent scanning method is improved, that is, in a relatively short time interval, only in the narrow track of (Vm-0.1Voc and Vm +0.1 Voc) scan 1. Vm and Voc of which are solar Array of maximum power point array voltage and open circuit voltage. Intervals for a longer period of time before the entire track in the context of the work of scanning one point.
Improvement after the intermittent scanning the track to maintain control of both the control accuracy have been raised to the stability of the system.
4 anti-island effect control methods
Island effect is due to electrical faults, misuse or natural factors caused the power grid power supply disruption at various client and the solar photovoltaic inverter network still operate independently of the phenomenon. Generally speaking, the island may effect the entire distribution system equipment and users of the adverse impact of equipment, including network and power inverter continuing crisis grid lines may be the lives and safety of maintenance personnel: interfere with the normal closing process grid: Beyond the control of the island in the power grid voltage and frequency. Users may cause damage to electrical equipment [5]. So to solve the photovoltaic system and network island issue is particularly important.
The author presents a positive feedback frequency of anti-disturbance island detection method. The main idea of this method is the first judgement of the current-voltage power grid frequency drift direction, and then periodically to impose the corresponding output current frequency of the disturbance. At the same time observing the actual output current frequency. When output current frequency following disturbances that signal changes in output current frequency and network inverter can be controlled, the disturbance of multiplying.To achieve the output current rapid changes in frequency and trigger anti-island frequency detection purposes.
5 experiment
The author of 500 W PV inverters and network were tested. By 8 rated at 50 W of polysilicon solar arrays thread, the input voltage to 100 VDC-170VDC, the output voltage of 220 VAC, the output frequency of 50 Hz. Enter the side table and amps were used to measure solar Table V input voltage and current, the output side by FLUKE 43B-power quality analyzer to detect and network exchange inverter output voltage and current parameters and waveforms. Since AC current output value is too small, so using the current probe around 8 on the turn after the measurement.
The results of the solar cell output voltage is basic in about 122 V, the output current of 2 A, a power output of 244 W. By the test results can be seen. The output voltage inverter to 230.9 V, output of 1.45 kW / 8 = 181.2W, so the efficiency of inverter to 0.74, inverter, including the efficiency of DC-DC and DC-AC transformation and the transformation of the auxiliary power Efficiency. Inverter output power factor of 0.97, basic network and maintain pressure with the same frequency and phase. The output current fundamental component of the current total of 99.6 percent, output of the power quality is satisfactory.
6 Conclusion
Waveform can be seen from the experiment, designed by the network of PV inverters work and stability. Good performance. As a result of a TMS320F240 type: DSP-based control circuit, the system has good dynamic response characteristics. With a maximum power of the anti-island track and control software design, which can make full use of solar energy and can detect the occurrence of island effect.